1. Field of the invention
The invention is based on a process and an apparatus for converting a greenhouse gas into a chemically or industrially utilizable substance or into a chemically or industrially utilizable mixture of substances.
2. Discussion of Background
The precharacterizing clauses of the claims of the invention relate to a prior art as is disclosed by DE 4 220 865 A1. There carbon dioxide, CO.sub.2, admixed with a substance containing hydrogen atoms, such as e.g. hydrogen gas, H.sub.2, water, H.sub.2 O, or hydrogen sulphide, H.sub.2 S, is subjected in a reactor to silent electric discharges which produce the fuels methane, CH.sub.4, and/or methanol, CH.sub.3 OH. The reactor contains a reaction accelerator in the form of a catalyst which contains copper and, if required, one or more of the metals Zn, Al, Mn, Cr, Ag, Mo, Ni or V. The catalyst may have been applied to a dielectric, to an electrode, to glass wool, quartz wool or rock wool, to ZrO.sub.2, Al.sub.2 O.sub.3, zeolite, silica gel or granular materials.
DE 4 332 790 A1 discloses a process for producing methanol from carbon dioxide and hydrogen in a thermal reactor which, in its bottom region, contains a copper-based catalyst. The temperature in the reaction chamber is between 220 and 250.degree. C., the pressure between 100 kPa and 2 MPa, the reaction mixture having a molar ratio of hydrogen to carbon dioxide in the range of from 1:1 to 1:10, preferably of 1:3. The residence time of the reaction mixture in the reaction chamber is between 0.1 s and 10 s, preferably 1 s.
These processes are not sufficiently efficient and, if hydrogen is used as the starting reactant, are still relatively expensive.
N. Boukhalfa et al., Conversion du CO.sub.2 en CO par decharge couronne dans des melanges air-CO.sub.2, Rev. Int. Hautes Temper. Refract. 26 (1990), pp. 39-48, disclose the acceleration of the conversion of CO.sub.2 into CO in a corona discharge by the catalytic action of nitrogen which is admixed to the reaction mixture as a constituent of air. A drawback of this process is that systems comprising a corona discharge are relatively bulky, expensive and consequently virtually unusable on a large industrial scale.
With respect to the relevant prior art reference is additionally made to a publication by B. Eliasson and U. Kogelschatz, Modeling and Application of Silent Discharge Plasmas, IEEE Transactions on Plasma Science, Vol. 19, No. 2, April 1991, pp. 309-323, which discloses a plurality of reactors arranged next to one another and above one another, involving silent electric discharge via a dielectric to generate ozone, which reactors can be employed in the present invention.